Costakid,
Good to hear that you're keeping fit.
I suppose that it really depends on your selfstyle with regard to fitness regimes, if you are sitting at a desk etc., then yes I can see the value of making regular visits to the gym.
For me ,well I'm on the 'go' most of the day, I arise about 6.30 everyday and have a fairly busy schedule,although I still manage to do a 3km walk each day, but I walk -don't run.
Although I'm long retired ( 77 next month ), I intend to keep going with my 'work' as long as I can, it does keep me reasonably physically fit, and importantly mentally alert, and I really enjoy the interaction with visitors to the museum and with my many 'students' who attend my English conversation and little craft groups.
I really wouldn't enjoy visiting a gym as I had more than my fair share of physical training when I was in the Navy, I was a 'Ganges ' boy at age 15, one year of non-stop gruelling physical activities from climbing the rigging of a 142 foot mast to hours of drilling as the 'Queens Guard ' and just about every sport that you could mention.
It was enough to put me off for life, however another 'Ganges' boy ,Duncan Bannatyne (also Dragons Den ), made a fortune from running gyms.
So do what you feel comfortable with is my best advice and everyone needs a hobby !!
Saludos,
Gordon